This invention relates to a magnetic disk, a method of manufacturing this magnetic disk and a magnetic disk apparatus including this magnetic disk.
The importance of magnetic disk apparatuses used as external storage units of computer systems has become greater in recent years and magnetic disk apparatuses have been improved in recording density year after year. Thin-film magnetic disks, provided as magnetic disks enabling such high-density recording apparatuses, have attracted a great deal of attention. Thin-film magnetic disks have a magnetic thin film instead of the conventional coating type medium formed in such a manner that a magnetic material prepared by mixing and kneading a magnetic powder and a binder is applied to a base.
Generally, thin-film magnetic disks (hereinafter referred to simply as "magnetic disk") with such a magnetic thin film have a structure described below. A base consisting of an aluminum alloy disk and a hard substrative layer formed on this disk is used. If a disk material having a large hardness, e.g., glass or the like, is used instead of an alluminum alloy, the base may be formed without any substrative layer. A magnetic layer is formed on the base. An intermediate layer may be formed between the magnetic layer and the base for the purpose of improving the adhesion therebetween and/or characteristics of the magnetic layer. A protective layer and, if necessary, a lubricating layer are formed on the magnetic disk, thus completing a magnetic disk.
A magnetic recording apparatus includes, as main components, a magnetic disk, a reading/writing magnetic head (hereinafter referred to simply as "head"), a magnetic disk rotating/controlling mechanism, a head positioning mechanism and a circuit for processing a read/write signal. In an ordinary reading/writing method for such a magnetic recording apparatus, the head and the magnetic disk are in contact with each other before the operation is started, but a very small spacing is created between the head and the magnetic disk when the magnetic disk is rotated, and recording or reproduction is performed in this state. To stop the operation, the rotation of the magnetic disk is stopped and the head and the magnetic disk are brought into contact again. This method is called a contact-start/stop method (hereinafter referred to as "CSS method"). For improvement in the recording density of the magnetic recording apparatus, it is preferable to reduce the extent of floating of the head during recording or reproduction. To maintain the desired head floating stability, a higher degree of flatness of the magnetic disk surface is required.
A frictional force caused between the head and the magnetic disk when the operation of the apparatus is started or stopped causes wear on each of the head and the disk, resulting in a deterioration in characteristics. If water or the like exists between the head and the magnetic disk when the magnetic disk is stopped, the head and the magnetic disk strongly attract each other. If the operation is started in such a state, there is a risk of a large force being caused between the head and the magnetic disk and, hence, damage to the head or the magnetic disk. Such frictional and attraction forces become greater as the flatness of the magnetic disk surface is increased, which effect conflicts with the above-mentioned requirement for the head floating stability with respect to the improvement in the recording density.
To reduce the frictional and attraction forces caused between the disk and the head, forming very small irregularities in the disk surface has been proposed. Japanese Patent Unexamined Publication 55-84045 discloses a magnetic disk on which a protective layer having a surface roughness of 20 to 50 nm is formed. Japanese Patent Unexamined Publication 56-22221 discloses a method of forming a protective layer with irregularities by sputtering through a mesh-like shielding plate. Japanese Patent Unexamined Publication 57-20925 discloses a magnetic disk having a protective layer having a surface on which very small projections are formed. Japanese Patent Unexamined Publication 58-53026 discloses a method of forming irregularities in a surface of a protective layer formed on a magnetic disk by irradiating the surface with gas ions. Japanese Patent Unexamined Publication 62-22241 discloses a method of forming irregularities in a surface of a protective layer formed on a magnetic disk by polishing, wet etching or dry etching so that the depth of irregularities is not greater than the thickness of the protective layer.
All these conventional magnetic disk and methods were provided for the purpose of reducing the frictional and attraction forces caused between the magnetic disk and the magnetic head, while the head sliding reliability and the head floating stability during use for a long time were not sufficiently considered.